1. Field of the Invention
The invention relates generally to mechanical stress within complementary metal oxide semiconductor (CMOS) structures. More particularly, the invention relates to structures and methods that provide mechanical stress within CMOS structures to enhance device performance and improve chip yield.
2. Description of the Related Art
CMOS structures comprise complementary mated pairs of field effect transistors of differing conductivity type. Due to the use of complementary mated pairs of differing conductivity type, CMOS structures also provide for reduced energy or power consumption.
A trend within CMOS fabrication is the use of stressed layers as a means to produce a mechanical stress or strain field within a channel region of a CMOS transistor. Certain types of mechanical stresses are desirable insofar as they introduce a stress into a semiconductor channel. Such a stress generally provides for enhanced charge carrier mobilities within a CMOS transistor. Complementary types of channel stress (i.e., tensile or compressive stress or strain in the direction of electrical current) enhance complementary types of charge carrier mobility (i.e., electron or hole) within complementary types of CMOS transistors (i.e., nFET or pFET).
Since mechanical stress is a significant factor that may considerably improve field effect transistor performance, CMOS structures and methods that provide for enhanced levels of mechanical stress within CMOS transistor channels are desirable.
Methods for improving charge carrier mobility within CMOS structures that include pFET and nFET devices are known in the semiconductor fabrication art. For example, En et al, in U.S. Pat. No. 6,573,172 teaches the use of a tensile stressed layer over a pFET device to provide a compressive stress of a pFET channel therein and a compressive stressed layer over an nFET device to cause a tensile stress of an nFET channel therein.
Since use of mechanical stress as a means to enhance charge carrier mobility is likely to continue within future generations of CMOS transistors, desirable are additional CMOS structures and methods for fabrication thereof that provide for charge carrier mobility enhancement incident to use of mechanical stress effects.